This invention relates to an arrangement for inducing pressurized film between rotating non-fixed location impellers or discs and adjacent sealing or thrust surfaces in turbine pumps and the like.
In the normal construction of a regenerative turbine pump, a disc-shaped impeller with the normal vanes milled in the periphery of the disc rotates within the confines of liners or heads. Typically the clearance between the sealing surfaces of the liners and the sealing surfaces of the impeller is in the order of 0.001 inch to 0.006 inch per side depending on the model and material of construction. A lesser clearance is provided when non-galling material is used, and on smaller models. A greater clearance is provided when galling material is used, and on larger models.
Because there is a difference in hydraulic pressure from one side of the impeller to the other (often a 1/2 to 1 pound difference), a non-fixed location impeller is forced to one side and into engagement with the liner, causing rubbing and wear and in the case of some galling materials, actual seizing of the pump. To alleviate this condition, it has been customary to drill "balancing" holes near the hub of the impeller to equalize the pressure. This solution has not been entirely successful because the spinning of the impeller offers too much resistance to the fluid flow. Forming the impeller with variously shaped slots close to the hub has also been attempted, but has not been entirely successful.
The most successful method of preventing galling has been to lock the impeller on the shaft with a nut on the end of the shaft or to use a lock collar to locate the impeller axially on the shaft in the instance of multi-stage pumps. The final adjustment is done with threaded collars on the shaft or in the housing or shiming. This, however, is a painstaking and costly process during manufacturing, assembly and in servicing of the unit. Varying temperatures and load conditions can cause differential expansion between the casing, frame and shaft. This makes wear and/or seizure likely.